# Tooth A: Primary Upper Right Second Molar

> In the Universal Numbering System, primary tooth A is the primary upper right second molar (primary maxillary right second molar). Its FDI (ISO 3950) designation is 55 and its Palmer designation is E in the upper right quadrant. It is a molar in the upper arch with typically 3 roots.

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Last verified: 2026-07-08

Neutral tooth-designation reference only; not clinical, diagnostic, or treatment advice. Root counts describe typical primary-tooth morphology and vary between individuals.

## Direct answer

- Which baby tooth is letter A? In the Universal Numbering System, primary tooth A is the primary upper right second molar (primary maxillary right second molar). Its FDI (ISO 3950) designation is 55 and its Palmer designation is E in the upper right quadrant. It is a molar in the upper arch with typically 3 roots.
- Universal letter: A
- FDI / ISO 3950 designation: 55
- Palmer designation: E UR
- Plain-language name: Primary Upper Right Second Molar
- Anatomical name: Primary Maxillary Right Second Molar
- Quadrant: Upper Right
- Arch and side: upper, right
- Type: molar
- Typical roots: 3

## Conversion table

| System | Designation |
| --- | --- |
| Universal Numbering System | A |
| FDI / ISO 3950 | 55 |
| Palmer notation | E UR |
| Tooth name | Primary Upper Right Second Molar |

## Search terms

- which baby tooth is letter a?
- tooth A
- tooth letter A
- baby tooth A
- primary tooth A
- primary upper right second molar
- primary maxillary right second molar
- fdi 55
- palmer E
- upper right tooth 5
- upper right molar

## Sources

- `TOOTH-1` American Dental Association — Universal Numbering System. <https://www.ada.org/publications/ada-news/2020/november/how-to-count-teeth-numbering-systems>
- `TOOTH-2` ISO 3950:2016 — Dentistry, designation system for teeth and areas of the oral cavity (FDI two-digit). <https://www.iso.org/standard/68292.html>
- `TOOTH-3` FDI World Dental Federation — two-digit notation. <https://www.fdiworlddental.org/>

## Related

- [Full tooth numbering chart](https://dentovio.com/tools/tooth-numbering-chart/index.html.md)
- [FDI to Universal converter](https://dentovio.com/tools/fdi-to-universal-converter/index.html.md)
- [Palmer notation converter](https://dentovio.com/tools/palmer-notation-converter/index.html.md)
- [Next tooth: Tooth B: Primary Upper Right First Molar](https://dentovio.com/tools/tooth-numbering-chart/tooth-b/index.html.md)